Some image-forming devices known in the art are provided with colorant (toner, ink, or the like) in a plurality of chromatic colors, such as cyan (C), magenta (M), and yellow (Y), and are capable of rendering gray by combining toner of these chromatic colors. In a printer calibration system disclosed in Japanese unexamined patent application publication No. 2007-150757, for example, a user outputs a gray patch via a server computer (personal computer), measures the color values (tristimulus values) of the patch with a colorimeter, creates calibration data based on these colorimetric values, and transmits the data to a printer. The printer then prints out images using the calibration data. In this way, the printer calibration system can prevent an upset in gray balance that may occur when the quantities of colorants used to form images fluctuate over time.
However, in order to prevent changes in gray colors with this conventional system, the calibration process must be executed frequently, leading to a large waste of colorant and time.